PROJECT SUMMARY Extensive research suggests the neuroendocrine system is sensitive to both chemical and non-chemical stressors. Polybrominated diphenyl ethers (PBDEs) are one class of endocrine disrupting chemicals with demonstrated ability to alter circulating levels of thyroid hormones, which are critical for normal brain development. Likewise, early-life exposure to psychosocial stressors has been associated with both disrupted endocrine system homeostasis and adverse neurodevelopmental endpoints. These results suggest PBDEs and social stressors operate through overlapping mechanisms, highlighting a plausible biologic pathway for interaction and underscoring the need to examine their integrated effects. However, research in this field has been impeded by a paucity of exposure assessment methods for quantifying social conditions, a topic area recently identified as a research gap and priority in the field of environmental health science. In the past decade telomeres, the repetitive, non-coding T2AG3 sequences located at chromosome ends, have emerged as a promising biomarker of social determinants, providing a potentially objective approach for examining the biological manifestation of social factors. We aim to advance this knowledge by investigating the relationship between pre and postnatal exposure to PBDEs and social adversity, measured using questionnaire data and telomere dynamics, on cognitive and behavioral performance. We will conduct this work using the existing infrastructure of the Columbia Center for Children's Environmental Health Mothers and Newborns Study, a longitudinal birth cohort of urban, minority mother-child dyads. This proposal is at the cutting edge of health disparities and environmental health research. We seek to answer critical questions for improving the health of low-income, minority populations, who often experience disproportionate exposure to both chemical and non- chemical stressors. The results will advance the current understanding of the complex etiologies underlying neurodevelopmental disorders, including the independent and interactive effects of social and environmental factors. This knowledge is critical for developing relevant public health policies and effective prevention and intervention strategies for reducing exposures and improving population health.